With LaDainian Tomlinson retiring this week, it once again brings up one of the most difficult questions in all of sports to answer

Who are the greatest running backs of all-time?

Do we look at career rushing yards that favors players who were consistently very good for a long period of time? Do we look the greatest single-seasons that may slant towards some players that were unable to maintain a high level over a long period of time? Do we consider a player's all-around game, or just running ability?

For this, we will try to weigh all these factors. While we use all-around career numbers, a player's individual seasons are considered in the context of their era, with the best seasons receiving more weight.

#20 Eric Dickerson

AP Images

Career Rushing Yards: 13,259

Total Touchdowns: 96

Seasons with AV* 15+: 3

Seasons with AV* 20+: 0

* AV=Approximate Value, a stat (via Pro-Football-Reference.com) that looks at a player's all-around game. The cut-offs here are somewhat arbitrary, but a season with an AV of 15 would be considered "Very Good," while an AV of 20 would be considered an "All-Time Great" season